The ABO blood group of 87 bacteriologically proven cases of cholera and 33 bacteriologically negative cholera-like diarrhoea cases was determined. When compared with the normal blood group distribution in the population of the Philippines of the same racial group to which the patients belonged, a relatively larger number of cases were found to occur in individuals of group O and a lesser number in those of group A. A plea is made for further studies on these lines to explain the host susceptibility in cholera and other acute enterotoxigenic diarrhoeas.